The present invention relates to a method of manufacturing a semiconductor integrated circuit device and more specifically to a semiconductor integrated circuit device manufacturing method having a process of forming a trench isolation.
The trench isolation is an element isolating part in a semiconductor substrate, which electrically isolates adjoining semiconductor integrated circuit elements by filling a groove formed between adjacent semiconductor integrated circuit elements with a specified burying material.
An example method of forming trench isolation examined by the inventor of this invention will be described below. After a groove is formed in a semiconductor substrate, an insulating film is formed on the inner surface of the groove. Then, a polycrystalline silicon film is deposited on the semiconductor substrate, after which the polysilicon film is etched back to fill only the groove with the polysilicon. After this, the semiconductor substrate is oxidized to oxidize the upper part of the polysilicon film in the groove, thus transforming the upper part into an insulating film.
An example method of burying an insulating film in the groove is disclosed in Japanese Patent Laid-Open No.143548/1983. The outline of this method is as follows. First, a side wall of an insulating film is formed on the inner wall surface of the groove to form a tapered surface on the inner wall surface of the groove, after which a burying insulating film is deposited over the semiconductor substrate. Next, the burying insulating film is etched back to bury the insulating film only in the groove.
The inventor of this invention, however, has found that the conventional art involves the following problems.
In the conventional art, by which a groove is filled with a polysilicon film and the upper part of the film is oxidized to ensure the insulating properties of the upper part of the polysilicon film in the groove, because there is a difference in the oxidiation rate of the polysilicon film in the groove between the periphery of the groove and the center, the thickness of the insulating film formed at the top of the polysilicon film is thinner at the groove periphery than at the central portion. As a result a recess in formed in the groove periphery, and in the subsequent process of forming conductor patterns, conductor film residue tends to remain in a recessed central part of the groove, leading to a short circuit between patterned conductors.
A conventional technique to solve this problem is proposed in Japanese Patent Laid-Open No. 149849/1991, which discloses a method of forming an insulating film to ensure the flatness of the top part of the polysilicon film before and after oxidizing the top part of the polysilicon film in the groove. This method, however, requires an additional process for forming an insulating film for ensuring the flatness.
The conventional technique of burying an insulating film in the groove is effective for the grooves with an aspect ratio of less than 1. As the aspect ratio becomes larger than 1, a problem arises that a cavity may form in the groove. This cavity is formed because the insulating film in the groove is coarse, the coverage of the groove is bad, and the film is not completely buried in the groove. This cavity appears on the top part of the groove causing a conductor film to remain during the subsequent process for forming a conductor pattern, with the result that the residual conductor film may short-circuit the patterned conductors.
An object of this invention is to provide a technique which allows a deep groove for a trench isolation to be filled completely without forming a dent or recess at the top of the filled groove.
Another object of this invention is to provide a technique which allows a deep groove for a trench isolation to be filled completely without forming a dent or recess at the top of the filled groove and without incurring a significant increase in the number of manufacturing steps.
A further object of this invention is to provide a technique which allows a deep groove for a trench isolation to be filled completely without exposing cavities from the top surface.
A further object of this invention is to provide a method of manufacturing a semiconductor integrated circuit device and more specifically to provide a technique which allows a deep groove for a trench isolation to be filled preferably without exposing cavities from the top surface and incurring a significant increase in the number of manufacturing steps.
These and other objects and novel features of this invention will become apparent from the following description in this specification and the accompanying drawings.
Representatives of the invention disclosed in this specification will be briefly summarized below.
A method of manufacturing a semiconductor integrated circuit device according to this invention comprises a step of forming in a semiconductor substrate a deep groove for a trench isolation with an aspect ratio larger than 1, a step of burying a first insulating film in the deep groove so that a shallow groove with an aspect ratio of not greater than 1 remains in the deep groove, and a step of depositing a second insulating film over the semiconductor substrate and removing an upper part of the second insulating film to planarize the upper part of the second insulating film buried in the shallow groove.
Further, a method of manufacturing a semiconductor integrated circuit device according to this invention forms a recess at the central part of the top surface of the first insulating film buried in the deep groove.
Further, a method of manufacturing a semiconductor integrated circuit device according to this invention comprises a step of forming in a semiconductor substrate a deep groove for a trench isolation with an aspect ratio larger than 1, a step of forming an insulating film on an inner wall surface of the deep groove and burying a semiconductor in the deep groove so that a shallow groove with an aspect ratio of not greater than 1 remains in the deep groove, and a step of depositing a second insulating film over the semiconductor substrate and removing the upper part of the second insulating film to planarize the upper part of the second insulating film buried in the shallow groove.
Further, the method of manufacturing a semiconductor integrated circuit device according to this invention forms a tapered portion in the opening portion of the deep groove.
According to the above-mentioned method of manufacturing a semiconductor integrated circuit device of this invention, the step of filling a deep groove for a trench isolation with a high aspect ratio is divided into two steps. In the first filling step, the deep groove is turned into a shallow groove by filling the deep groove to a specified extent to lower the aspect ratio. In the second filling step, the shallow groove is filled and the upper part of the filling material in the shallow groove is planarized. These steps makes it possible to fill a deep groove preferably without causing cavities to appear on the upper part of the deep groove, without forming a recess in the outer periphery of the upper part of the deep groove, and without incurring a significant increase in the number of manufacturing steps.
Further, according to the above-mentioned method of manufacturing a semiconductor integrated circuit device of this invention, by forming a recess in the central portion of the upper surface of the first insulating film buried in the deep groove, a certain thickness of the second insulating film buried in the shallow groove can be ensured at the central upper part of the first insulating film, so that even if a cavity is formed in the center of the first insulating film, it is possible to prevent a large recess or a groove communicating with the cavity in the center of the first insulating film from being formed at the center of the second insulating film.
Further, according to the above-mentioned method of manufacturing a semiconductor integrated circuit device of this invention, a tapered portion is formed in the opening part of the deep groove. This makes it possible to bury a second insulating film in the shallow groove without forming any cavities.